Model for uptake of organic chemicals by plants Public Deposited

Published May 1990. Facts and recommendations in this publication may no longer be valid. Please look for up-to-date information in the OSU Extension Catalog:


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Abstract or Summary
  • Uptake, in-plant transport, and local accumulation of organic chemicals by plants are influenced by plant characteristics, properties of the chemical and the soil, and by environmental conditions. Evaluations of plant contamination required by regulatory agencies cannot be made experimentally for the many thousands of xenobiotic chemicals in existence or being developed. A predictive simulator in the form of a mathematical model would provide a valuable tool for such evaluations. For this reason, a mathematical model (UTAB, uptake, Translocation, Accumulation, Biodegradation) was formulated by defining a generic plant as a set of adjacent compartments representing the major pools involved in transport and accumulation of water and solutes. The model consists of one root compartment, three stem compartments, and three leaf compartments. Each compartment is subdivided into two transport compartments, one for xylem and one for phloem, and a storage compartment. In addition, two compartments model the root volume outside the Casparian strip, one for the apparent free space and one for the cell volume. Values for the anatomical dimensions of the compartments and for physical and chemical coefficients were chosen from the literature. The complete system of equations, which describes uptake and accumulation, consists of 24 differential equations which are solved in terms of the chemical mass in each compartment as a function of time. The solution procedure is also developed and presented. For calibration purposes, concentrations measured in roots, stems, and leaves were compared with model predictions, while model parameters were changed until no further improvement in matching model predictions with experimental results was obtained. This exercise revealed important plant behavior that was not accounted for in the original formulation of the model and, as such, showed the value of the model for elucidating plant response. The model satisfactorily predicted the observed uptake and distribution patterns for bromacil in soybean plants, at the stage of growth and under the environmental conditions used in the experiments, involving a range of transpiration rates. This indicates that the model is flexible enough to provide an accurate representation of uptake and the influence of transpiration rate on the uptake and translocation of this chemical. Parameter values used in the model were selected from literature and experimental observation. They functioned well in these simulations and they are appropriately applied in the model. The chemical parameters for storage, mobilization, and diffusion when used in the model also yielded satisfactory results, suggesting that they are also appropriately applied. Finally, the calibration, although of limited scope, showed that the model equations yielded an accurate picture of the actual uptake patterns for bromacil in soybeans used in these experiments. The theoretical exercise of compiling the model is shown to be a constructive step in learning how to predict the fate of xenobiotic contamination in plants. The model shows excellent promise for future use. However, additional testing and validation are needed.
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